This invention relates to the inspection of welds between tubes and tube plates as arise for example in heat exchangers used for steam generation in nuclear reactors. The tubes may be directly welded to the tube plate or, alternatively, indirectly through the agency of an external sleeve.
In the former case, the welds may develop faults such as defect cracks from time to time and a method of repair has become established. The method involves inserting a repair sleeve inside the tube and explosively welding one end of the sleeve to the tube plate and brazing the other end of the sleeve to the inside wall of the tube. This by-passes the weld and superficially removes the faulty weld from any further consideration. However, in practice a requirement exists to monitor or inspect periodically and rapidly the faulty weld as, despite its fault, it nevertheless serves as a back-up for the strength and leak security of the repair sleeve and the behaviour of the defect in this weld indicates the stresses which exist in the assembly and the likely condition of the interspace between the tube and the sleeve. The fact that the weld is now covered by the sleeve makes close access for inspection impossible.
The same considerations arise in the type of heat exchanger where, during construction, the tube is welded to the tube plate via an external sleeve, ie. there is a requirement for the weld to be inspected periodically and, in practice, such inspection must necessarily be carried out from the interior of the tube.